Va'eira

Shemos 6,13 Rashi- Hashem told Moshe to Treat Pharaoh with the honor befitting a king when he speaks to him. Why is this the place where Hashem tells him that? This isn't the first time he's being told to go to Pharaoh. Logically, the place to tell Moshe should be in 3,18 before Moshe goes to Pharaoh for the first time!